This invention relates to a method for the production of a fluorine-containing aromatic derivative, and more particularly to a fluorine-containing aromatic derivative useful for industrial applications.
In recent years, the reaction which, by the introduction of a perfluoroalkyl group into the molecule of an organic compound, produces a partially fluoro compound exhibiting useful properties relative to physiological activities is attracting attention.
This invention, as described above, is directed to a method for the production of a fluorine-containing aromatic derivative. For the perfluoroalkylation of aromatic compounds, various methods have been disclosed.
For example, the synthesis of a fluorine-containing aromatic derivative by the reaction of a fluorine-containing aliphatic iodide with a halogen-substituted aromatic compound under the action of ultrasonic waves in the presence of zinc powder and a palladium type catalyst (Japanese Patent Disclosure SHO No. 58(1983)-92627) and the method resorting to what is known as Ullman reaction, such as, for example, the production of 2-trifluoromethyl naphthalene by the reaction of 2-iodonaphthalene with trifluoromethyl iodide in pyridine as a solvent in the presence of copper powder as a catalyst at 120.degree. C. (Journal of Japan Chemical Society, No. 11, 1976, page 1791) have been reported.
These methods are not advantageous commercially because they have drawbacks, specifically the former method suffering from high cost of the palladium catalyst and inevitably requiring use of ultrasonic waves and the latter method entailing difficulty in the preparation of copper powder of high catalytic activity and suffering the yield of product to be governed by the amount of the catalyst used.
The synthesis of a fluorine-containing aromatic derivative by the direct thermal reaction of a fluorine-containing aliphatic iodide with an aromatic compound instead of the aforementioned cross-coupling reaction using a metal complex has been reported (Journal of Fluorine Chemistry, Vol. 17, page 345 (1981)).
This method, however, does not provide commercially advantageous production of the derivative because the yield of the product is low (about 50%) and further because the reaction proceeds only at a high temperature (about 200.degree. C.) and requires much time (about 50 hours) for its completion.
With a view to alleviating reaction conditions, the method of introducing a perfluoroalkyl group into aromatic compound by directly fluorinating (R.sub.f -IF.sub.2) a fluorine-containing aliphatic iodide (R.sub.f -I) with fluorine gas, then treating the resultant fluorination product with sulfonic acid (CF.sub.3 SO.sub.3 H) and benzene (PhH) or fluorobenzene thereby forming a salt (1), and causing this salt (1) to react with an aromatic compound (ArH) as shown by the following formula (1) has been reported (Journal of Organic Synthetic Chemical Society, Vol. 41, No. 3, page 251 (1983)). ##STR1##
This method again proves commercially disadvantageous in respect that the aforementioned salt (1) is thermally instable, the synthesis is difficult to carry out, and the synthesis requires use of a special device.
Besides the methods described above, the reaction which uses heptafluorobutyryl peroxide as a perfluoroacyl peroxide and .rho.-methoxy toluene and .rho.-dimethoxybenzene derivative as aromatic compounds has been reported (the Journal of Organic Chemistry, Vol. 48, page 4908 (1983)).
In an aromatic compound having two or more substituents as described above, particularly a poly-substituted aromatic compound having attached thereto such an electron-donating group as methoxy group, the product of the introduction of a heptafluoropropyl group (n--C.sub.3 F.sub.7 --) is obtained in a low yield owing to the reaction of electron transfer with the heptafluorobutyryl peroxide and conversely the product of the introduction of an ester group ##STR2## is obtained in a high yield. Particularly when the aromatic compound is .rho.-dimethoxybenzene, 1,4-dimethyl-2,5-dimethoxybenzene, or 1,4-di-t-butyl-2,5-dimethoxybenzene, absolutely no product incorporating a heptafluoropropyl group is obtained and, instead, a product incorporating an ester group is obtained in a yield exceeding 90%.
Thus, no method has been available for commercially advantageous production of a fluorine-containing aromatic derivative by the introduction of a perfluoroalkyl group into an aromatic compound. The desirability of developing a method capable of commerically advantageously producing a fluorine-containing aromatic derivative has found widespread acceptance.